The air/fuel ratio used during the operation of a combustion appliance can affect the efficiency and emissions of the combustion appliance. Example combustion appliances include furnaces, water heaters, boilers, direct/in-direct make-up air heaters, power/jet burners and any other residential, commercial or industrial combustion appliance. In many cases, the flow of gas is adjusted to set the air/fuel ratio. This is often accomplished by modulating a gas valve to control the pressure and thus the flow of gas to the combustion appliance. In some cases, the gas valve is modulated based on signals from one or more pressure or flow sensors placed in the gas and/or air streams. In some cases, turbulent and/or otherwise non-uniform gas and/or air flows can introduce noise into the pressure or flow sensor signals, which can result in a non-uniform or otherwise non-optimal air/fuel ratio. This can reduce the efficiency and/or increase the emissions of the combustion appliance. What would be desirable is an improved air/gas admittance device that provides a more uniform gas and/or air flow to reduce sensor noise and thus improve the efficiency and/or emissions of a combustion appliance.